Production of butadiene



June 19, 1945. w. J. MAT-rox PRODUCTION OF BUTADIENE Filed Feb. 1l, 1942 copolymerization process.

Patented June 19,1945 y UNITED STATES PATEN'Iy orrici:I

PRODUCTION F BUTADIENE William J. Mattox, Chicago, Ill., -assignor to Universal Oil Products Company, Chicago, Ill., a

corporation of Delaware This is a continuation in part of my co-pending application, Serial No. 348,976, filed July 31, 1940.

This invention relates to a process for the catalytic'cracking and dehydrogenation of hydrocarbon fractions to producezdiolens, particularly butadiene.

One of the most important processes for the production of synthetic rubber is the butadiene polymerization process or the butadiene-styrene Processes, therefore, which result in the formation of reasonably large quantities of butadiene are particularly importantsince the Iproduction of syntheticrubber is at present limited by the production of butadiene.

I have found that by cracking hydrocarbon K fractions comprising essentially Cs to C12 hydrocarbons, mainly oleiins, that relatively large amounts of normal C4 olefins can be produced and that these C4 olefins may be readily converted to butadieneI by dehydrogenation, preferably catalytic. I have found, furthermore,'that one of the most suitable charging materials for the catalytic cracking step to produce normal butenes is polymer gasoline formed by polymerization of Cz, Caand C4 olens. I have also found that isobutene, which is produced to some extent by the cracking and dehydrogenation steps, and 'which cannot readily be converted to butadiene, may be`isomerized to normal butenes by contacting it with a cracking catalyst at moderately high temperatures. Therefore, I propose a combination catalytic cracking and dehydrogenation process in which high yields of butadiene may be obtained from an olenic charging stock by converting the higher` boiling olefins to normal C4 olefins followed by dehydrogenation of the C4 olens to butadiene, with return of the-unconverted C4 hydrocarbons, including isobutene, to the cracking step.

In one specific embodiment, the present invention comprises a process for the production of butadiene which comprises catalytically cracking a hydrocarbon oil comprising essentially Ce to C12 hydrocarbons, mainly olefms, to produce lower boiling olens, separating from the resultant Referring now to the drawing, a hydrocarbon fraction consisting essentially of Cs to C12 hydrocarbons, mainly olefins, is supplied through line I, valve2, pumpv 3, line 4 and valve 5 to heating coil 6 disposed in furnace 'I wherein the hydrocarbon oil is heated. to a temperature in the range of from about 750 to 1150 F., preferably about 50 to 1100 F. and at a pressure that may vary from slightly superatmospheric to 100 pounds or more per square inch. The resulting heated hydrocarbons are supplied through line 8 and valve 9 to catalytic reactor I0 wherein they are contacted with a cracking catalyst for a suillcient length of time to result in the formation of lower boiling olens, particularly C4 olens.

Catalytic reactor l0 may be either of the type in which heat is supplied to the catalytic mass by means of a. heat convective medium or it may be of the type in which substantially all of the heat of reaction is supplied to the reaction by means of the high heat content of the incoming oil. Catalytic reactor III contains, preferably, a bed of catalyst consisting essentially of an association of silica and alumina, the catalyst being either a naturally occurring compound or synthetically prepared. The catalyst may be granular and arranged in beds so that the flow of the hydrocarbon vapors is conducted down'through the beds or the catalyst may be in the powdered form, maintained in a turbulent state by an upwardly rising stream of hydrocarbon vapors.

Regeneration of the catalyst is usually nec- `eSSal`y and Such regeneration may be accomproducts a fraction comprising -butenes and a higherv boiling fraction, returning said higher boiling fraction for further catalytic cracking, dehydrogenating said fraction comprising butenes in the presence of a dehydrogenating catalyst. to produce butadiene, separating butadiene from the resultant conversion products and returning the remaining C4 hydrocarbons including isobutene to the aforementioned catalytic cracking treatment to isomerize said isobutene rto normal butenes.

The accompanying` drawing illustrates diagrammatirally in side elevation one specic form of apparatus that may be employed in accomplishing the objects of this invention,

plished in situ by the passage of oxygen containing gases through the catalytic mass. If desired, however, the catalyst may be removed either periodically or continuously and regenerated in a separate regeneration zone. ,Y

Returning now to the drawing, conversion vproducts from reactor I0 are supplied through line Il and valve I2 into fractionator I3 wherein a fraction consisting of Cs and lighter hydrocarbons, a fraction comprising C4 hydrocarbons, andv a higher boiling fraction are separated. The light fraction is withdrawn through line I4 and valve I5 and the heavy fraction is returned to the catalytic cracking step through line I6 and valve I1 and line I5. The C4 fraction which consists not only of normal butenes but also of isobutene and butanes is withdrawn from fractionator I3 through line' Il, valve I9, pump 20, line 2|, and valve 22 and is supplied to heating coil 23 contained in furnace 24 wherein the C4 fraction is heated to dehydrogenating conditions. The resulting heated hydrocarbonsv are supplied through line ..25 and valve 28 to dehydrogenation reactor 21 wherein they are contacted with a dehydrogenation catalyst to effect dehydrogenation of a portion thereof to butadiene. A

Reactor 2'I may be of the type in which the hydrocarbon vapors are passed through a bed of I granular dehydrogenation catalyst orit may be of the type in which the hydrocarbon vapors are passed upward through a turbulent bed of powdered catalyst. In either case, it is usually desirable that the reactor be equipped with heat exchange surfaces so that the endothermic heat of dehydrogenation may be supplied to the reactants etherein.

The catalyst which is preferred for the dehy.. drogenation comprises chromium oxide on a support such as activated alumina. However, it should be noted that many other catalysts such as vanadium oxide, molybdenum oxide and the like have been found quite suitable. Furthermore, other supports such as clay and magncsia have been found suitable, although not usually as satisfactorily as activated alumina.

In the reactor it is usually desirable that the temperatures be maintained within the range of from about 1000 F.'to about l300 ll'. although in some cases it is 'possible to eilect dehydrogenation above or below the preferred temperature range. Furthermore, it is desirable and. in fact, necessary in order to prevent undue decomposition, to employ low pressures in the dehydrogenation reactor. It is usually'desirable that the partial pressure of the hydrocarbons undergoing reaction be maintained below about- 300 mm. mercury absolute and it is preferred, in fact, that the hydrocarbon partial pressure be held below about 200 mm. mercury absolute.l Under these conditions, high yields of butadiene may be obtained without excessive carbon formation and without undesirable side reactions occurring to any great extent.

The reaction products from dehydrogenation tion from a lighter fraction comprising Ci and lighter materials and a heavier fraction comprising Cs and heavier materials. The lighter fraction is withdrawn and the heavier fraction is returned to the catalytic cracking treatment. The

and the remaining C4 fraction, comprisingr a Qarge reactor 21 are supplied through line 20 and valve 29 to butadiene separation zone 30 in which a separation is eifected between butadiene, other C4 hydrocarbons, and C3 and lighter products. It is usually necessary in order to obtain a reasonably pure butadiene to employ not only 'the customary absorption and stripping methods to separate a C4 fraction from lighter and heavier prodprocess through line 33 and valve Il. The re maining C4 hydrocarbons, a large proportion of which is isobutene, are withdrawn from the separation zone through line 35 and valve I! and proportion of isobutene, is returned to the catalytic cracking step .to isomerize the isobutene to normal butenes.

E claim: l

l. A process for the production of butadiene which comprises subjecting an olefinic distillate at cracking conditions to the action of a cracking catalyst to form C4 oleilns, subjectingresultant C4 olens at dehydrogenating conditions to the action of a dehydrogenating catalyst to form butadiene incidental to which a minor quantity of isobutene" is formed, separating from the resultant conversion products a butadiene fraction and a fractionv comprising unconverted C4 oleflns and the isobutene, supplying the latter fraction to the cracking step, whereby to isomerize the isobutene into normal butene, and supplying the normal butene thus formed to the dehydrogenating step together with the C4'oleiins produced by the catalytic cracking.

2. .The process of claim 1 further characterized in that the olefinic distillate comprises polymer gasoline.

3. A process for the production of butadiene which comprises subjecting an'olenic distillate at cracking conditions to the action of a cracking catalyst to form C4 olei'lns, subjecting resultant C4 olens at dehydrogenating conditions to the action pf a dehydrogenating catalystto form butadiene incidental to which a minor quantity are returned to the catalyticcracking step. The

Example` n A polymer gasoline consisting predominantly of C through Cio oleflns is heated to adtteinperature of about 930 F. and contacted with a synthetic silica-alumina catalyst prepared by compositing silica hydrogel with alumina hydrogtl followed bye. calcination treatment." The resulting prod- -ucts of reaction of which C4 olens are a large,y I

porportion arefractionated Ato separate a C4 fracof isobutene is formed, supplying isobutene thus formed to the catalytic cracking step, whereby to yeil'ect conversion thereofinto normal butene, and supplying the normal butenethus formed to the dehydrogenating step together with the C4 olens produced by the catalytic cracking.

4. The process of claim 3 further characterized in thatthe cracking catalyst comprises a synthetlc composite comprising silica and alumina. 5. The Iprocess of claim 3 further characterized in that the olefnic/distillate comprises polymer gasoline.

6. A 'process for the productionof butadiene which comprises subjecting polymer gasoline at cracking conditions to the action of a cracking catalyst to eiect conversion thereof into/C4 oleflns as the principal reaction, subjecting resultant C4 oleilns at dehydrogenating conditions to the actionof a dehydrogenating catalyst to form butadiene incidental to which a minor quantity of isobutene is formed, supplying isobutene thus formed to the catalytic cracking step,.whereby to eect conversion thereof into normal butene, and

supplying the normal butene thus formed to the dehydrogenating step together with thev C4 cieiins produced by the catalytic cracking. 

